Research Article: Impact of Four Years of Annual Mass Drug Administration on Prevalence and Intensity of Schistosomiasis among Primary and High School Children in Western Kenya: A Repeated Cross-Sectional Study

Date Published: May 12, 2018

Publisher: The American Society of Tropical Medicine and Hygiene

Author(s): Bernard O. Abudho, Eric M. Ndombi, Bernard Guya, Jennifer M. Carter, Diana K. Riner, Nupur Kittur, Diana M. S. Karanja, W. Evan Secor, Daniel G. Colley.


Schistosomiasis remains a major public health problem in Kenya. The World Health Organization recommends preventive chemotherapy with praziquantel (PZQ) to control morbidity due to schistosomiasis. Morbidity is considered linked to intensity of infection, which along with prevalence is used to determine the frequency of mass drug administration (MDA) to school-age children. We determined the impact of annual school-based MDA on children across all primary and high school years using a repeated cross-sectional study design in five schools near Lake Victoria in western Kenya, an area endemic for Schistosoma mansoni. At baseline and for the following four consecutive years, between 897 and 1,440 school children in Grades 1–12 were enrolled and evaluated by Kato-Katz for S. mansoni and soil-transmitted helminths (STH), followed by annual MDA with PZQ and albendazole. Four annual rounds of MDA with PZQ were associated with reduced S. mansoni prevalence in all school children (44.7–14.0%; P < 0.001) and mean intensity of infection by 91% (90.4 to 8.1 eggs per gram [epg] of stool; P < 0.001). Prevalence of high-intensity infection (≥ 400 epg) decreased from 6.8% at baseline to 0.3% by the end of the study. Soil-transmitted helminth infections, already low at baseline, also decreased significantly over the years. In this high prevalence area, annual school-based MDA with high coverage across all Grades (1–12) resulted in rapid and progressive declines in overall prevalence and intensity of infection. This decrease was dramatic in regard to heavy infections in older school-attending children.

Partial Text

Human schistosomiasis is a snail-transmitted trematode infection caused by any of five species in the genus Schistosoma. Globally, approximately 700 million people are at risk of this infection.1,2 More than 240 million people in 78 countries are estimated to be infected with schistosomes. More than 90% of the cases occur in sub-Saharan Africa, where the infection is estimated to cause more than 200,000 deaths annually.3,4 In Kenya, both Schistosoma mansoni and Schistosoma haematobium remain serious public health concerns with approximately 6 million people infected and an additional 15 million being at high risk of the infection in endemic areas of the country.5Schistosoma mansoni infection is common in the western part of Kenya and its prevalence shows an inverse relationship with the distance from Lake Victoria.6,7

Baseline data from the present study of primary and secondary school children indicate that S. mansoni infection was prevalent among untreated school children in the Asembo Bay area of western Kenya. Although almost half of the children were infected with S. mansoni, most had light to moderate intensities of infection. In general, fewer than 10% were heavily infected (≥ 400 epg). Presently, WHO guidelines recommend annual school-based MDA with PZQ in areas where prevalence of infection is ≥ 50%. Where the prevalence of infection is less than 50% but at or more than 10%, current recommendations call for school-based MDA every other year, whereas if prevalence is less than 10% infection, MDA twice during primary school is considered sufficient.13 In addition, the prevalence of heavy infection is recommended by WHO as a guide for when to move from morbidity control to elimination as a public health problem and then on to elimination of transmission. When the prevalence of heavy infection is ≥ 5% in sentinel sites, morbidity control is considered to be still in order, and countries would be eligible for elimination as a public health problem when heavy infection prevalence is less than 1% in all sentinel sites.13 The data presented here regarding heavy infections in school children may contribute to potential re-evaluations of some of these targets, guidelines, and goals.




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